Thrown when a mixin with infix
but is done with a composer that cannot be used for mixin.
;1 but A;CATCH ;# OUTPUT: «X::Mixin::NotComposable: Cannot mix in non-composable type A into object of type Int␤»
The compile-time equivalent of this error is X::Composition::NotComposable
Returns the target of the failed mixin operation.
Returns the thing that could not act as a role for mixing it in